348 Prof. Draper on the Allotropism of Chlorine 
The points which this memoir is intended to establish are,— 
I. That chlorine gas can exist under two forms. In the same 
way that metallic iron can exist as active or passive iron, chlorine 
can assume the active or passive state. 
II. Having established the fact of the allotropism of chlorine, I 
shall then show its connexion with the theory of substitutions of 
M. Dumas, and how the most remarkable points in that theory 
may be easily accounted for. 
The time, perhaps, has not yet arrived for offering a complete 
mechanical explanation of the assumption of an active or passive 
state. It may be remarked, that a very trivial modification of our 
admitted views of the relation between atoms and their proper- 
ties, is all that is required to give a consistent explanation of every 
one of these facts. Instead of regarding the specific qualities of 
an atom as appertaining equally to the whole of it in the aggre- 
gate, we have merely to assume that there is a relation between 
its properties and its sides, and that any foree which can make 
it change its position upon its own axis will throw it into the ac- 
tive or passive state. But this is nothing more than the well 
known idea of the polarity of atoms. 
Phenomena of the Decomposition of Water by Chlorine in the 
Rays of the Sun. 
From the various facts which might be employed as offering 
the means of establishing the allotropism of chlorine, I shall select 
those which arise from an examination of the phenomena of -the 
decomposition of an aqueous solution of chlorine by the rays of 
the sun. 
For many years it has been known that an aqueous solution of 
chlorine undergoes decomposition by the aid of the solar rays. 
Several of the most remarkable phenomena connected with this 
decomposition appear to have been overlooked. Among such 
may be mentioned the singular fact, that chlorine which has 
been thus influenced by the sun has obtained the quality of ef- 
fecting this decomposition subsequently, to a measured extent, 
even in the dark. Not to anticipate what I have to offer on this 
point, I shall now proceed in the first place to establish the va- 
rious facts connected with the decomposition in question. 
Having provided a number of small glass vessels, consisting of 
a bulb and neck of the capacity of from 1:5 to 2-0 cubic inches, 
